(1) Field of the Invention
The present invention relates to a reusable liquid filter assembly and more particularly to a reusable liquid filter assembly for use with an engine for discharging filtered liquid to the engine. In a preferred embodiment, the filter assembly is a reusable oil filter for mounting on or near an internal combustion engine.
(2) Description of the Prior Art
Filter units for filtering liquid, such as oil or fuel, are known in the art. An oil filter unit is typically placed in the oil line of an internal combustion engine to remove grit and other contaminants from the lubricating oil to provide longer engine life and improved engine performance.
The typical oil filter unit has a cannister or housing for coupling to the engine with a filter element therein for filtering the oil as it circulates through the cannister. The cannister ordinarily has one end adapted for coupling onto the engine block of the internal combustion engine by means of an internally threaded nipple that threads onto a corresponding externally threaded nipple or matching connecting configuration on the block. Oil inlet holes surround the nipple for receiving oil from the engine, and filtered oil is returned to the engine through the nipple. A gasket surrounds the inlet holes and the nipple to seal the unit against the block.
After the filter unit has been in the oil line for a certain period of operation, approximately 2,000 miles or so for the typical engine operated under routine conditions, the gradual accumulation of grit and other contaminants in the filter element begins to reduce the efficiency and effectiveness of the filter unit and also provide increasing resistance to oil flow therethrough.
If the resistance to oil flow reaches a predetermined level, a pressure sensitive bypass valve is activated so that the oil bypasses the filter element and is returned essentially unfiltered to the engine. It is important for the operation and longevity of the engine that the filter unit be replaced or serviced before this valve is actuated and the engine is lubricated by unfiltered oil. However, were it not for the bypass valve, the filter element might clog, oil flow through the filter unit and likewise through the engine would cease, and oil starvation accompanied by engine failure would result.
Disposable or throw-away type oil filter units are known in the prior art. U.S. Pat. No. 3,265,213 to Decker et al. discloses such a filter unit. When the filter element has become clogged, the entire unit is removed and discarded, and a new unit is put in its place. This type of filter unit is relatively expensive in that a whole new unit must be used each time the filter unit is serviced, even though only the filter element itself has been expended and the other parts of the filter unit have not yet exceeded their useful life.
Also, with such a disposable filter unit, the filter element and bypass valve are sealed therein, and it is not easy to determine when the element has become clogged. It is possible for the filter to be completely expended after only 1,500 miles of engine operation, whereas the recommended procedure for the typical internal combustion engine calls for oil filter unit changes approximately only every 5,000 to 6,000 miles. It is also possible, due to faulty manufacturing or mishandling, for the bypass valve to become lodged in the "open" position even when the filter is new, thereby giving no oil filtering protection at all. Because the filter unit is completely sealed, it can be difficult to determine whether the bypass valve is operating properly.
An oil filter unit having a detachable cover permitting replacement of the filter element itself is known in the art. U.S. Pat. No. 3,036,711 to Wilhelm shows such a filter unit.
The prior art oil filter units are disadvantageous in that expense is increased, because the entire filter unit or the filter element itself must be periodically replaced with a new unit or element. Also, the flow of oil through the filter element may be restricted because of the manner in which the filter element is mounted inside the filter unit. It also may not be readily determinable by visual inspection whether the bypass valve is operating properly.
Furthermore, the oil filter units of the prior art are typically manufactured to fit only one type or several limited types of engines. The internally threaded nipples vary in diameter and thread size, the filter unit itself may vary in size and shape, and the coupling on the engine block with which the unit must mate may vary in size and shape. Such filter units are therefore not readily interchangeable between different internal combustion engines. Accordingly, a dealer or service station operator ordinarily must keep a variety of types and sizes of oil filter units in stock.